Techniques for color-based tracking of faces or hands often assume a static skin color model. However, skin color perceived by a camera can change when lighting changes. In common real environment multiple light sources impinge on the skin. Therefore, for robust skin pixel detection, a dynamic skin color model that can cope with the changes must be employed. We show that skin detection in video can be enhanced by exploiting the knowledge of the range of possible skin colors for the camera used. In normalized color coordinates, this range has a distinct shape we call the skin locus. We developed an adaptive histogram back-projection technique where the skin color model is updated by pixels in the search region, which fall in the skin locus. We demonstrate increased detection capability with web-cam videos of faces taken successively under daylight, incandescent lamp, fluorescent light and a combination of these light sources.